Three-way microvalve device and method of fabrication

ABSTRACT

A three-way (3-way) Micro-Electro-Mechanical Systems (MEMS)-based micro-valve device and method of fabrication for the implementation of a three-way MEMS-based micro-valve are disclosed. The micro-valve device has a wide range of applications, including medical, industrial control, aerospace, automotive, consumer electronics and products, as well as any application(s) requiring the use of three-way micro-valves for the control of fluids. The discloses three-way micro-valve device and method of fabrication that can be tailored to the requirements of a wide range of applications and fluid types, and can also use a number of different actuation methods, including actuation methods that have very small actuation pressures and energy densities even at higher fluidic pressures. This is enabled by a novel pressure-balancing scheme, wherein the fluid pressure balances the actuator mechanism so that only a small amount of actuation pressure (or force) is needed to switch the state of the actuator and device from open to closed, or closed to open.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.14/872,202 filed Oct. 1, 2015, incorporated herein in its entirety byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under FA8651-13-C-0267awarded by the Air Force. The government has certain rights in theinvention.

FIELD OF INVENTION

The present invention is directed to a three-way (3-way)Micro-Electro-Mechanical Systems (MEMS)-based micro-valve device and amethod of fabricating the device. The present invention involves a novelfeature of using the fluid under control of the micro-valve to pressurebalance the actuator and thereby enable small actuation forces to openand close the device. The present invention has a wide range ofapplications, including medical, industrial control, aerospace,automotive, consumer electronics and products, as well as anyapplication(s) requiring the use of three-way micro-valves for thecontrol of fluids.

BACKGROUND OF THE INVENTION

A number of MEMS-based micro-valves have been reported in the literatureusing a variety of actuation methods, including: pneumatic;electrostatic; thermo-pneumatic; shape-memory alloy (SMA); thermalbimetallic; piezoelectric; and electromagnetic.

All of these micro-valves previously reported in the literature havebeen 2-way devices that can merely “open” or “close” to allow the deviceto “turn on” or “turn off” the flow of fluid through the structure.Importantly, none of these devices can be operated as three-waymicro-valves that can direct the flow of fluid in a preferred direction.This is partly due to the fact that MEMS is, in general, a relativelynew technology, and specifically because MEMS-based micro-valves areeven less mature. Consequently, the only available method for theimplementation of a fluidic system wherein the fluid can be directed toa preferred direction has been to use at least a quantity of at leasttwo (2) separate two-way micro-valves. However, this is an expensivesolution that doubles the power required, size, weight and space, aswell as reduces reliability, and therefore is not an optimal orpreferred solution for many applications.

A major challenge for MEMS-based actuators in general, and micro-valvesin particular, is the very low actuation forces that can be generated onthe small dimensional size scales of the actuator elements. Theresulting small actuation forces typically prevent these types ofdevices to be used where the actuator must overcome larger forces. Forexample, a typical electrostatically-actuated micro-valve will onlygenerate less than a 1 psi (pound per square inch) of actuationpressure. Therefore, if the micro-valve actuator must overcome the fluidpressure in order to open and/or close the device to the flow of fluid,then the micro-valve would be restricted to applications where the fluidpressures are smaller than the actuation pressure, which is less than 1psi.

Disclosed herein is a three-way micro-valve device and method offabrication that can be tailored to the requirements of a wide range ofapplications. The disclosed 3-way micro-valve can use a number ofdifferent actuation methods, including actuation methods that have verysmall actuation pressures while being able to control fluid pressuresmuch higher than the pressures that can be generated by the actuator.The micro-valve of the present invention employs a pressure balancingscheme so that it can be actuated while controlling fluid pressures muchlarger than the actuation pressure generated by the actuator.

SUMMARY OF INVENTION

The present invention is directed to a three-way (3-way)Micro-Electro-Mechanical Systems (MEMS)-based micro-valve device andmethod of fabrication for the implementation of a three-way MEMS-basedmicro-valve. The present invention has a wide range of applications,including medical, industrial control, aerospace, automotive, consumerelectronics and products, as well as any application(s) requiring theuse of three-way micro-valves for the control of fluids.

A major challenge for MEMS-based actuators in general, and micro-valvesin particular, is the very low actuation forces that can be generated onthe small dimensional size scales of the actuator elements. Theresulting small actuation forces typically prevent these types ofdevices to be used where the actuator must overcome larger forces. Forexample, a typical electrostatically-actuated micro-valve will onlygenerate less than a 1 psi (pound per square inch) of actuationpressure. Therefore, if the micro-valve actuator must overcome the fluidpressure in order to open and/or close, then the microvalve would berestricted to applications where the fluid pressures are smaller thanthe actuation pressure, that is, less than 1 psi

The present invention allows for the implementation of a three-waymicro-valve device and method of fabrication that can be tailored to therequirements of a wide range of applications and fluid types. The 3-waymicro-valve disclosed can also use a number of different actuationmethods, including actuation methods that have very small actuationpressures and energy densities even at higher fluidic pressures. This isenabled by a novel pressure-balancing scheme wherein the fluid pressurebalances the actuator mechanism so that only a small amount of actuationpressure (or force) is needed to switch the state of the actuator anddevice from open to closed, or closed to open.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are an illustration of a three-way micro-valve withtwo inlet ports and one outlet port, and showing two functional statesof the device.

FIGS. 2(a) and 2(b) are an illustration of a three-way micro-valve withone inlet port and two outlet ports, and showing two functional statesof the device.

FIG. 3 is a table showing the possible states of a three-way micro-valvehaving two inlet ports and one outlet port. These states are applicableto the three-way micro-valve of FIGS. 1(a) and 1(b).

FIG. 4 is a table showing the possible states of a three-way micro-valvehaving one inlet port and two outlet ports. These states are applicableto the three-way micro-valve of FIGS. 2(a) and 2(b).

FIGS. 5(a) - 5(c) are cross sectional drawings of a pressure-balanced,normally-open, electrostatically-actuated, three-way micro-valve withtwo inlet ports and one outlet port.

FIGS. 6(a) and 6(b) are cross sectional drawings of a pressure-balanced,normally-closed, electrostatically-actuated, three-way micro-valve withtwo inlet ports and one outlet port.

FIGS. 7(a) and 7(b) are cross sectional drawings of a pressure-balanced,normally-closed, piezoelectrically-actuated, three-way micro-valve withtwo inlet ports and one outlet port.

FIGS. 8(a)-8(h) are cross sectional drawings illustrating thefabrication process of the bottom substrate and the movable membraneused for implementation of the pressure-balanced,electrostatically-actuation three-way micro-valve.

FIGS. 9(a)-9(e) are cross sectional drawings illustrating thefabrication process of the top substrate used for implementation of thepressure-balanced, electrostatically-actuated three-way micro-valve.

FIGS. 10(a)-10(b) are cross sectional drawings illustrating thefabrication process for the implementation of process pressure-balanced,electrostatically-actuated three-way micro-valve, wherein the top andbottom substrates are joined together to form the micro-valve.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a three-way (3-way)Micro-Electro-Mechanical Systems (MEMS)-based micro-valve device andmethod of fabrication for the implementation of a three-way MEMS-basedmicro-valve. The present invention has a wide range of applications,including medical, industrial control, aerospace, automotive, consumerelectronics and products, as well as any application(s) requiring theuse of three-way micro-valves for the control of fluids.

The present invention allows for the implementation of a three-waymicro-valve device and method of fabrication that can be tailored to therequirements of a wide range of applications and fluid types. Thethree-way micro-valve disclosed herein can also use a number ofdifferent actuation methods, including actuation methods that have verysmall actuation energy densities, and still be able to control the flowof fluids even at higher fluidic pressures. This is enabled by a novelpressure-balancing scheme wherein the fluid pressure balances theactuation so that only a small amount of actuation force or pressure isneeded to switch the state of the actuator and device, even when thefluid pressure is much larger than the pressure that can be generated bythe actuator.

FIGS. 1(a) and 1(b) and FIGS. 2(a) and 2(b) illustrate the functionalityof the three-way micro-valve of the present invention. The micro-valvehas three (3) fluidic ports (that is, openings into or out of the devicestructure through which fluid that is either a gas or a liquid or acombination of gas and liquid, can flow) with two (2) differentmicro-valve device configurations, with the first device configurationshown in FIGS. 1(a) and 1(b) and the second in FIGS. 2(a) and 2(b).

In one micro-valve device configuration 10, as shown in FIGS. 1(a) and1(b), the micro-valve device 11 has two inlet fluidic ports, inlet portone, numbered 12 in FIGS. 1(a) and 1(b), and inlet port two, numbered 13in FIGS. 1(a) and 1(b), that are used as inlet ports, thereby allowingfluid to flow into the micro-valve 11. That is, fluid can flow into themicro-valve device 11 through these inlet ports 12 and 13, through themicro-valve 11, and into, and through the remaining port, outlet portthree, numbered 16 in FIGS. 1(a) and 1(b), if these ports are in an“open” state.

Inlet port1, numbered 12 in FIGS. 1(a) and 1(b), is connected to inletfluid conduit 14, which is a fluid pathway into inlet port one 12 andthe micro-valve device 11 in FIGS. 1(a) and 1(b). Outlet port three,numbered 16 in FIGS. 1(a) and 1(b), is connected to outlet fluid conduit17 that is a fluid pathway out of the micro-valve device 11. Inlet porttwo, numbered 13 in FIGS. 1(a) and 1(b), is connected to fluid conduit15 and is a fluid pathway into inlet port two 13 and the micro-valve 11in FIGS. 1(a) and 1(b).

The micro-valve device 11 shown in FIGS. 1(a) and 1(b) has a fluidicswitching mechanism 18, whereby either inlet port one, numbered 12 inFIGS. 1(a) and 1(b), or inlet port two, numbered 13 in FIGS. 1(a) and1(b), is connected to outlet port three, numbered 16 in FIGS. 1(a) and1(b). This fluidic switching mechanism 18 is shown in two of theswitched states with the first switched state illustrated in FIG. 1(a)wherein inlet port one, numbered 12 in FIGS. 1(a) and 1(b), isfluidically connected to outlet port three, numbered 16 in FIGS. 1(a)and 1(b). That is, fluid can flow from conduit 14, through inlet portone 12, through the micro-valve 11, through the outlet port 16, andsubsequently through conduit 17. In the state shown in FIG. 1(a), inletport two, numbered 13 in FIGS. 1(a) and 1(b), is not connected to outletport three, numbered 16 in FIGS. 1(a) and 1(b). That is, no fluid isallowed from conduit 15, through the inlet port two 13 and into themicro-valve 11, and therefore no fluid can flow through conduit 17 frominlet port two 13.

In the second switched state shown in FIG. 1(b), inlet port two,numbered 13 in FIGS. 1(a) and 1(b), is fluidically connected to outletport three, numbered 16 in FIGS. 1(a) and 1(b) by the fluid switch 18 ofthe microvalve 11. That is, fluid can flow from conduit 15, through theinlet port two 13, through the microvalve 11, through the outlet port16, and subsequently through conduit 17. In the state shown in FIG. 1b ,inlet port one, numbered 12 in FIG. 1, is not connected to outlet portthree, numbered 16 in FIGS. 1(a) and 1(b). That is, no fluid is allowedfrom conduit 14, through the inlet port one 12 and into the microvalve11, and therefore no fluid can flow through conduit 17 from inlet portone 12.

In the second device configuration, as shown in FIGS. 2(a) and 2(b), themicrovalve device 21 has one inlet fluidic port, inlet port one,numbered 26 in FIGS. 2(a) and 2(b), that is used as an inlet port, thatis, fluid can flow into the microvalve device 21 through this inlet port26. There are two outlet fluidic ports, with outlet port one numbered 22in FIGS. 2(a) and 2(b), and outlet port two numbered 23 in FIGS. 2(a)and 2(b). These outlet ports 22 and 23 are used as outlet ports 22 and23, whereby fluid can flow out of the microvalve device 21 that enteredthrough inlet port one 26. Inlet port one, which is numbered 26 in FIGS.2(a) and 2(b), is connected to inlet fluid conduit 27 that is a fluidpathway into the microvalve device 21. Outlet port one, which isnumbered 22 in FIGS. 2(a) and 2(b), is connected to outlet fluid conduit24 that is a fluid pathway out of the microvalve device 21. Outlet porttwo, which is numbered 23 in FIGS. 2(a) and 2(b), is connected to outletfluid conduit 25 that is a fluid pathway out of the microvalve device21.

The microvalve device 21 shown in FIGS. 2(a) and 2(b) has a switchingmechanism 28 whereby the inlet port, which is numbered 26 in FIGS. 2(a)and 2(b), is connected to either outlet port one, numbered 22 in FIGS.2(a) and 2(b), or outlet port two, numbered 23 in FIGS. 2(a) and 2(b).

This switching mechanism 28 is shown in two states, with the firstswitched state illustrated in FIG. 2(a) wherein the inlet port, numbered26 in FIG. 2(a), is fluidically connected to outlet port one, numbered22 in FIG. 2(a). That is, fluid can flow from conduit 27, through theinlet port 26, through the micro-valve 21, through the outlet port one22, and subsequently through conduit 24. In the state shown in FIG.2(a), the inlet port, numbered 26 in FIG. 2(a), is not connected tooutlet port two, numbered 23 in FIG. 2(a). That is, no fluid is allowedfrom conduit 27, through the micro-valve 21, and through conduit 25.

In the second switched state of FIGS. 2(a) and (b), shown in FIG. 2(b),the inlet port, numbered 26 in FIG. 2(b), is fluidically connected tooutlet port two, numbered 23 in FIG. 2(b) by the micro-valve 21 switchmechanism 28. That is, fluid can flow from conduit 27, through the inletport 26, through the micro-valve 21, through the outlet port two 23, andsubsequently through conduit 25. In the state shown in FIG. 2(b), inletport one, numbered 26 in FIG. 2(b), is not connected to outlet port one,numbered 22 in FIG. 2(b). That is, no fluid is allowed from conduit 27,through the microvalve 21, and through conduit 24.

As can be seen from FIGS. 1(a) and 1(b) and FIGS. 2(a) and 2(b), themicro-valve is able to control the direction of the fluid from the inletport(s) and conduit(s) to the outlet port(s) and conduit(s).

In general, the 3-way micro-valve of the device configuration of FIGS.1(a) and 1(b), with two inlet ports and one outlet port, will haveseveral possible states, as shown in the table 30 of FIG. 3, dependingon which of the inlet ports and outlet port are either in an “on” or“off” state. As can be seen, five (5) of these states are essentiallyequivalent, in that no fluid is allowed to flow through the micro-valvedevice. Specifically, these are states 2, 3, 4, 5, and 8. Additionally,state 1, wherein fluid flows through the device with all ports open, isnot of much interest since this state can be obtained without thepresence of a valve by just having a branching from port 1 to ports 2and 3. The two (2) states of primary interest are states 6 and 7 wherebythe fluid can flow from inlet port 1 to outlet port 3 in State 6 andState 7, where the fluid can flow from inlet port 2 to outlet port 3.

Similarly, the 3-way micro-valve of the device configuration of FIGS.2(a) and 2(b), with one inlet port and two outlet ports, also hasseveral possible states, as shown in the table 40 of FIG. 4, dependingon which of the inlet ports and outlet port are either in an “on” or“off” state. As in the previous case, there are five (5) states thatallow no fluid to flow through the device. Specifically, these arestates 3, 4, 5, 7, and 8. Additionally, state 1, wherein fluid flowsthrough the device with all ports open, is not of much interest sincethis state can be obtained without the presence of a valve by justhaving a branching from ports 1 and 2 to port 3. The two (2) states ofprimary interest are states 2 and 6 whereby the fluid can from inletport 1 to outlet port 2 in State 2 and State 6 where the fluid can flowfrom inlet port 1 to outlet port 3.

It is important to note that valves in general, and micro-valves inparticular, may not exhibit all of the states shown in FIGS. 3 and 4.The ability of these devices to exhibit specific states is dependent onthe specific design of the device, method of actuation, as well as otherfactors. Nevertheless, as noted above, many of the states are redundant(e.g., the “no flow” states) or have no particular interest inapplications (e.g., the state with all ports open) and therefore theability of a micro-valve device to exhibit less than all possible statesis not limiting in most applications.

Another differentiating element of 3-way micro-valves is whether theyare “normally open” or “normally closed.” “Normally open” and “normallyclosed” describe the state or position of the valve when no actuationsignal is applied to the device. That is, the natural or resting stateof the device when no electrical power is applied to the device'sactuator. Typically, a “normally closed” device would employ some kindof spring or mechanical force that results in the valve port or portsbeing closed when no power is applied to the micro-valve actuator.Conversely, a “normally open” micro-valve's ports are open when no poweris applied. Whether the micro-valve is normally “open” or normally“closed” will depend on the exact design of the micro-valve, as well asthe application requirements. The 3-way micro-valves of the presentinvention can be implemented in both the “normally open” or “normallyclosed” device configurations.

Typically, the actuation method employed in any micro-valve design isdictated by the requirements of the intended application. Typicallythese requirements would include: maximum flow rate, maximum pressuredifferential, operating temperatures, electrical power; size and weight;type of fluid to be controlled; as well as other factors.

The specific device requirements of a particular application willtypically allow the number of viable actuation methods to be reduced.For example, in applications where the operational temperatures arerelatively low or vary over a large range, the use of any type ofthermally-initiated actuation methods such as thermal bimetallic,shape-memory alloy (SMA), and thermo-pneumatic may not be a good choicesince all of these methods require heating of the actuator, andadditionally, the actuator itself is temperature sensitive.

For example, shape-memory alloy and thermo-pneumatic actuators operateby heating an actuator material to induce a phase change, and therefore,the phase change temperature would have to be higher than the maximumoperational temperature. Therefore, the operational temperatures are animportant determiner of the choice of actuation method. Nevertheless,thermally-initiated actuation methods may have some significantadvantages in some applications. For example, shape-memory alloy (SMA)actuators have several advantages compared to other actuation schemes,including: the actuation energy densities of SMA actuators are typicallyvery high compared to other actuation methods and this allows thecontrol of fluids at large pressure differentials; and the maximumallowable mechanical strains of SMA actuators are also very high (i.e.,some SMA actuators have reported repeatable strain levels of around 8%)thereby enabling larger strokes and consequently larger flow rates atmodest differential pressures. Thermo-pneumatic actuators also have veryhigh actuation energy densities, but typically do not have large strokessince it is considered prudent to limit the strain levels of thematerials used in the actuator to below 1%.

Often a very important criterion for selection of actuation method isthe power requirements for the specific application. For example, forsome applications the heating requirements of thermal-actuation methodsmay exceed the maximum desired device power requirements.

Additionally, pneumatic actuation approaches wherein an externalpressure generator is required to provide pressures to actuate thedevice will increase the size (and power requirements) of the deviceconsiderably. Therefore, for some applications pneumatic actuation maynot be an optimal approach.

Electromagnetic actuation is a popular method of actuation inmacro-scale valves, but this type of actuation does not scale well tothe MEMS size domain. Many MEMS-based electromagnetic actuation schemesrequire a meso-scale electromagnetic solenoid that must be attached tothe valve mechanism and this increases the cost and size of the systemconsiderably, and therefore, this actuation method may not be desirablefor some applications. Alternatively, some MEMS-based electromagneticactuation schemes attempt to integrate wire windings into the devicestructure, but this makes the fabrication very challenging and themaximum current that can be safely passed through small wires oftenlimits the electromagnetic forces that can be generated using thisapproach.

Electrostatic and piezoelectric actuation methods are often employed formicro-valve devices. However, it is important to note that both of theseapproaches have small inherent strokes. That is, the amount ofdeflection of the actuator during actuation is relatively small. Theresultant effect of a small stroke of the micro-valve is that the fluidflow pressure through the opening will be high in order to overcome flowresistance created by the small stroke, and therefore, this may limitthe amount of fluid flow through the device when in an “open” state.

Another important point about electrostatic actuation is that theactuation energy densities or actuation pressures that can be generatedusing this actuation method are very small. The consequence of this isthat a device using this actuation scheme may not be able to operate,that is actuate to open and/or close, at differential fluid pressureshigher than can be generated by this type of actuator.

Piezoelectric actuation schemes, on the other hand, can generate verylarge actuation energy densities, and therefore, can be used inapplications requiring operation at high differential fluid pressures.Typically, electrostatic actuation schemes are simpler to implementcompared to piezoelectric actuation schemes. In fact, as a general rule,electrostatic-based actuation schemes will be the simplest to implementsince it requires no additional or exotic materials such as in the casefor shape-memory alloys, thermo-pneumatics, bimetallics andpiezoelectrics.

The important point about actuation schemes for MEMS-based microvalvesis that the requirements of the specific application will often dictatethe type of actuator that can be used. The three-way micro-valve devicesdisclosed herein of the present invention can be used with any of theavailable actuation schemes.

Pressure-Balanced Three-Way Microvalve.

The first embodiment of a three-way micro-valve 50 of the presentinvention is shown in FIGS. 5(a)-5(c). The three-way microvalve 50 shownin FIGS. 5(a)-5(c) is electrostatically-actuated and alsopressure-balanced as described herein. In FIG. 5(a), the micro-valve isshown an un-actuated state with both inlet port one and inlet port twoboth in an “open” state and connected to the outlet port so that fluidcan flow through both of these ports and through the micro-valve outletport. In FIG. 5(b) the device is shown in an actuated state with inletport two in an “open” state and connected to the outlet port therebyallowing fluid to flow through inlet port two, through the micro-valve,and through the outlet port. In FIG. 5(b), inlet port one is in a“closed” state and does not allow fluid to flow through this port. InFIG. 5(c) the micro-valve device is shown in the alternative actuatedstate with inlet port one “open” and connected to the outlet portwhereby fluid is allowed to flow through inlet port one, through themicro-valve, and through the outlet port. In FIG. 5(c), inlet port twois in a “closed” state and does not allow fluid to flow through thisport.

The micro-valve 50 shown in FIG. 5(a) is shown in the un-actuated state,that is, with no power applied to the actuator. The micro-valve 50 hastwo inlet ports, inlet port one 54 and inlet port two 53. There is oneoutlet port 57. In the un-actuated state shown in FIG. 5(a), themicro-valve 50 has both inlet ports, 53 and 54, fluidically connected tothe outlet port 57.

The micro-valve 50 shown in FIG. 5(a) is composed of a bottom substratelayer 56 that is electrically conductive, a top substrate layer 55 thatis also electrically conductive, and a middle substrate layer 62 that iselectrically conductive. An electrically insulating layer 58electrically insulates the top substrate layer 55 from the middlesubstrate layer 62, and an electrically insulating layer 59 electricallyinsulates the bottom substrate layer 56 from the middle substrate layer62. The micro-valve device 50, has a fluidic chamber 51 wherein thefluid to be controlled by the micro-valve 50 can pass through. Insidethe flow chamber 51 of the micro-valve 50, the middle substrate layer 62has been made thinner and essentially is a membrane 64 that ismechanically compliant. That is, the membrane 64 can be deflected underthe action of an actuation force of sufficient magnitude. The membrane64 is also electrically conductive and is electrically connected to theelectrically conductive middle substrate layer 62. The membrane 64 hasopenings 52 that fluidically connect the top portion of the microvalvechamber 51 to the bottom portion of the microvalve chamber 51 and alsofluidically connect the inlet ports, 53 and 54, to the outlet port 57when the micro-valve 50 is not actuated as shown in FIG. 5(a).Additionally, depending on the exact details of the microvalve 50 designthe membrane 64 may be patterned in various shapes and sizes in order toobtain specific design requirements.

As shown in FIG. 5(a), the middle substrate layer 62 is connected to anelectrical terminal 61. Additionally, the top substrate layer 55 isconnected to an electrical terminal 60, and the bottom substrate layeris connected to an electrical terminal 63. Importantly, in FIG. 5(a),none of the electrical terminals, either 60, 61 or 63, are connected toan applied voltage, since the micro-valve shown in FIG. 5(a) is in anun-actuated state.

The microvalve 50 shown in FIGS. 5(a)-5(c) has sealing rings (orsurfaces or valve seats), 66 and 67, the purpose of which is to reduceor eliminate leakage of fluid through the ports when the valve is in aclosed position. The sealing rings 66 and 67 also help to reducestiction effects, whereby the membrane 64 stays stuck to the sealingrings 66 or 67 when it is desired that the membrane 84 separate from thesealing rings 86 or 87.

An actuated state of the micro-valve is shown in FIG. 5(b). An appliedvoltage potential V 65 is applied across electrical terminal 60connected to the top substrate layer 55 and electrical terminal 61connected to the middle substrate layer 62, which is also electricallyconnected to the membrane 64. The polarity of the applied voltage 65shown in FIG. 5(b) has the positive side of the voltage potential 65applied to terminal 60 and the negative side of the voltage potential 65applied to terminal 61. However, the applied voltage 65 can be reversedwith the same effect on actuation of the micro-valve 50. Additionally,one side of the applied voltage potential 65 could be connected toground also with the same effect on actuation of the micro-valve 50.

When an electrical voltage potential is applied across the terminals 60and 61 of the micro-valve 50, as shown in FIG. 5(b), electrostaticcharges (not shown) will develop on the top substrate layer 55. Theseelectrical charges will be mirrored on the middle substrate layer 62 andthe membrane 63. That is, electrical charges of equal magnitude andopposite polarity (not shown) to the electrical charges on the topsubstrate layer 55 will develop in the middle substrate layer 62 andalso the membrane 64.

These electrostatic charges on the top substrate layer 55 and the middlesubstrate layer 62 that is electrically connected to the membrane 64,result in an electrostatic force of attraction (not shown) to developbetween the top substrate layer 55 and the membrane 64. Since themembrane 64 is substantially mechanically compliant, the membrane 64under the electrostatic forces of attraction will deflect towards thetop substrate layer 55 if the electrostatic forces are larger than themechanical stiffness of the membrane 64. If the applied voltagepotential 65 across electrical terminals 60 and 61 is sufficiently largein magnitude, the membrane 64 will be pulled toward and eventually touchthe sealing ring 66. This is the so-called “electrostatic pull-inphenomena.” The electrically insulating layer 58 will prevent electricalshorting of the electrostatically-charged membrane 64 and theelectrostatically-charged top substrate layer 55. The touching of themembrane 64 to the insulating layer 58 on the sealing ring 66 of the topsubstrate 55 is shown in FIG. 5(b). When the membrane 64 makessufficient contact to the sealing ring 66, the micro-valve is in a fullyactuated state, whereby the inlet port one 54 is closed to the flow offluid, as shown in FIG. 5(b). In this actuated state, inlet port two 53is open and fluid can flow into this port, through the micro-valve 50bottom part of the chamber 51, through the openings 52 in the membrane64, through the top part of the micro-valve 50 chamber 51, and throughthe outlet port 57. Therefore, in this state, inlet port one 54 isclosed to fluid flow, inlet port two 53 is open to fluid flow, andoutlet port 57 is open to fluid flow.

An alternative actuated state of the micro-valve is shown in FIG. 5(c).An applied voltage potential V 68 is applied across electrical terminal63 connected to the bottom substrate layer 56 and electrical terminal 61connected to the middle substrate layer 62 that is also electricallyconnected to the membrane 64. The polarity of the applied voltage 68shown in FIG. 5(c) has the positive side of the voltage potential 68applied to terminal 63 and the negative side of the voltage potential 68applied to terminal 61. However, the applied voltage 68 can be reversedwith the same effect on actuation of the micro-valve 50. Additionally,one side of the applied voltage potential 68 could be connected toground also with the same effect on actuation of the micro-valve 50.

When an electrical voltage potential is applied across the terminals 63and 61 of the micro-valve 50, as shown in FIG. 5(c), electrostaticcharges (not shown) will develop on the bottom substrate layer 56. Theseelectrical charges will be mirrored on the membrane 64. That is,electrical charges of equal magnitude and opposite polarity (not shown)to the electrical charges on the bottom substrate layer 56 will developon the membrane 64.

These electrostatic charges on the bottom substrate layer 56 and themiddle substrate layer 62 that is electrically connected to the membrane64, result in an electrostatic force of attraction (not shown) todevelop between the bottom substrate layer 56 and the membrane 64. Sincethe membrane 64 is substantially mechanically compliant, the membrane 64under the electrostatic force of attraction will deflect towards thebottom substrate layer 56 if the electrostatic forces are larger thanthe mechanical stiffness of the membrane 64. If the applied voltage 68across electrical terminals 63 and 61 is sufficiently large inmagnitude, the membrane 64 will be pulled toward and eventually touchthe bottom sealing ring 67. This is the so-called “electrostatic pull-inphenomena.” The electrically insulating layer 59 will prevent electricalshorting of the electrostatically-charged membrane 64 and theelectrostatically-charged bottom substrate layer 56. The touching of themembrane 64 to the insulating layer 59 is shown in FIG. 5(c). When themembrane 64 makes sufficient contact to the bottom sealing ring 67, themicro-valve is in a fully actuated state, whereby the inlet port two 53is closed to the flow of fluid. In this actuated state, inlet port one54 is open and fluid can flow into this port, through the micro-valve 50top part of the chamber 51, through the openings 52 in the membrane 64,through the top part of the micro-valve 50 chamber 51, and through theoutlet port 57. Therefore, in this state, inlet port two 53 is closed tofluid flow, inlet port one 54 is open to fluid flow, and outlet port 57is open to fluid flow.

As pointed out above, an important feature of the micro-valve 50 shownin FIGS. 5(a)-5(c) is the pressure-balancing scheme of the device 50.Specifically, the inlet fluid pressure inside the micro-valve 50 chamber51 is present on both sides of the membrane 64 and therefore appliesequal fluid pressure over both surfaces of the membrane 64 with theresult that the fluid pressure is balanced over both sides of themembrane 64. Therefore, if the fluid pressure is balanced as shown inFIG. 5(a), the micro-valve can be actuated, as shown in FIGS. 5(b) and5(c), with an actuation pressure that is substantially less than thepressure of the fluid. This is useful when an actuation method haslimited amounts or levels of actuation pressure that is available. Thisis particularly useful when electrostatic actuation is used thatinherently has very limited amounts or levels of actuation pressure thatcan be generated with this actuation method. Noteworthy is that withoutthe feature of pressure-balancing as shown in FIG. 5(a), the actuationmethod would have to overcome the mechanical stiffness of the membrane64 and the pressure of the fluid, which can be substantial. However,with pressure balancing, even if the pressure of the fluid is many timeslarger in magnitude than the electrostatic pressure that can begenerated during actuation, the micro-valve 50 membrane can still beactuated as shown in FIGS. 5(b) and 5(c).

An alternative embodiment of a three-way micro-valve 70 of the presentinvention is shown in FIGS. 6(a) and 6(b). The three-way micro-valve 70shown in FIGS. 6(a) and 6(b) is electrostatically-actuated and alsopressure-balanced, as described herein. In FIG. 6(a), the micro-valve 70is shown an un-actuated state with inlet port one in an “open” state andconnected to the outlet port, thereby allowing fluid to flow throughinlet port one, through the micro-valve, and through the outlet port. Inthis state, inlet port two is in a “closed” state and no fluid can flowthrough this port. In FIG. 6(b), the micro-valve 70 is shown actuatedstate with inlet port two in an “open” state and connected to the outletport, thereby allowing fluid to flow through inlet port two, through themicro-valve, and through the outlet port. In this alternative state,inlet port one is in a “closed” state and no fluid can flow through thisport.

The micro-valve 70 shown in FIG. 6(a) is shown in the un-actuated state,that is, with no power applied to the actuator. The micro-valve 70 hastwo inlet ports, inlet port one 74 and inlet port two 73. There is oneoutlet port 77. In the un-actuated state shown in FIG. 6(a), themicro-valve 70 has inlet port one 74 fluidically connected to the outletport 77 and inlet port two 73 is closed to the flow of fluid through theport and consequently through the micro-valve 70.

The micro-valve 70 shown in FIG. 6(a) is composed of a bottom substratelayer 76 that is electrically conductive, a top substrate layer 75 thatis also electrically conductive, and a middle substrate layer 82 that iselectrically conductive. An electrically insulating layer 78electrically insulates the top substrate layer 75 from the middlesubstrate layer 82, and an electrically insulating layer 79 electricallyinsulates the bottom substrate layer 76 from the middle substrate layer82. The micro-valve device 70, has a fluidic chamber 71 wherein thefluid to be controlled by the micro-valve 70 can pass through. Insidethe flow chamber 71 of the micro-valve 70, the middle substrate layer 84has been made thinner and essentially is a membrane 84 that ismechanically compliant. That is, the membrane 84 can be deflected underthe action of an actuation force of sufficient magnitude. The membrane84 is also electrically conductive and is electrically connected to theelectrically conductive middle substrate layer 82. The membrane 84 hasopenings 72 that fluidically connect the inlet port one 74 to the outletport 77 when the micro-valve 70 is not actuated as shown in FIG. 6(a).Additionally, depending on the exact details of the microvalve 70 designthe membrane 84 may be patterned in various shapes and sizes in order toobtain specific design requirements.

As shown in FIG. 6(a), the middle substrate layer 82 is connected to anelectrical terminal 81. Additionally, the top substrate layer 75 isconnected to an electrical terminal 80 and the bottom substrate layer 76is connected to an electrical terminal 83. Importantly, in FIG. 6(a),none of the electrical terminals, either 80, 81 or 83, are connected toan applied voltage since the micro-valve shown in FIG. 6(a) is in theun-actuated state.

The micro-valve 70 shown in FIGS. 6(a) and 6(b) has sealing rings (orsurfaces or valve seats), 86 and 87, the purpose of which is to reduceor eliminate leakage of fluid through the ports when the valve is in aclosed position. The sealing rings 86 and 87 also help to reducestiction effects, whereby the membrane 84 stays stuck to the sealingrings 86 or 87 when it is desired that the membrane 84 separate from thesealing rings 86 or 87.

An actuated state of the micro-valve is shown in FIG. 6(b). An appliedvoltage potential V 85 is applied across electrical terminal 80electrically connected to the top substrate layer 75 and electricalterminal 81 electrically connected to the middle substrate layer 82 thatis also electrically connected to the membrane 84. The polarity of theapplied voltage 85 shown in FIG. 6(b) has the positive side of thevoltage potential 85 applied to terminal 80 and the negative side of thevoltage potential 85 applied to terminal 81. However, the appliedvoltage 85 can be reversed with the same effect on actuation of themicro-valve 70. Additionally, one side of the applied voltage potential85 could be connected to ground also with the same effect on actuationof the micro-valve 70.

When an electrical voltage potential is applied across the terminals 80and 81 of the micro-valve 70 as shown in FIG. 6(b), electrostaticcharges (not shown) will develop on the top substrate layer 75. Theseelectrical charges will be mirrored on the middle substrate layer 82 andthe membrane 84. That is, electrical charges of equal magnitude andopposite polarity (not shown) to the electrical charges on the topsubstrate layer 75 will develop in the middle substrate layer 82 andalso the membrane 84.

These electrostatic charges on the top substrate layer 75 and the middlesubstrate layer 82 that is electrically connected to the membrane 84,result in an electrostatic force of attraction (not shown) to developbetween the top substrate layer 75 and the membrane 84. Since themembrane 84 is substantially mechanically compliant, the membrane 84under the electrostatic force of attraction will deflect towards the topsubstrate layer 75 if the electrostatic forces are larger than themechanical stiffness of the membrane 84. If the applied voltage 85across electrical terminals 80 and 81 is sufficiently large inmagnitude, the membrane 84 will be pulled toward and eventually touchsealing ring 86. This is the so-called “electrostatic pull-inphenomena.” The electrically insulating layer 78 will prevent electricalshorting of the electrostatically-charged membrane 84 and theelectrostatically-charged top substrate layer 75. The touching of themembrane 84 to the insulating layer 78 on the sealing ring 86 is shownin FIG. 6(b). When the membrane 84 makes sufficient contact to thesealing ring 86, the micro-valve 70 is in a fully actuated state wherebythe inlet port one 74 is closed to the flow of fluid. In this actuatedstate, inlet port two 73 is open and fluid can flow into this port,through the micro-valve 70 bottom part of the chamber 71, through theopenings 72 in the membrane 84, through the top part of the micro-valve70 chamber 71, and through the outlet port 77. Therefore, in this state,inlet port one 74 is closed to fluid flow, inlet port two 73 is open tofluid flow, and outlet port 77 is open to fluid flow.

The micro-valve 70 shown in FIG. 6(b) can be returned to the un-actuatedstate, shown in FIG. 6(a), by turning off or removing the appliedvoltage potential 85. When the voltage potential 85 is removed, theelectrostatic charges on the top substrate layer 75 and the membrane 84dissipate and the force of attraction between the top substrate layer 75and the membrane 84 diminishes and eventually goes to zero. In thiscondition, the mechanical stiffness of the membrane 84 will becomelarger than the electrostatic force of attraction as the electrostaticforces of attraction diminish and the membrane 84 will return to theun-deflected state as illustration in FIG. 6(a).

As noted above, an important feature of the micro-valve 70 shown inFIGS. 6(a) and (b) is the pressure-balancing scheme of the device 70.Specifically, the inlet fluid pressure inside the micro-valve 70 fluidchamber 71 is present on most of both sides of the membrane 84 with theexception of the area inside the sealing ring 87 of inlet port two 73.Consequently, there is a nearly equal fluid pressure over both surfacesof the membrane 84 with the result that the fluid pressure (and force)is nearly balanced over both sides of the membrane 84. Therefore, if thefluid pressure is balanced as shown in FIGS. 6(a) and 6(b), themicro-valve can be actuated, as shown in FIG. 6(b) with an actuationpressure that is substantially less than the pressure of the fluid. Thisis useful when an actuation method has limited amounts or levels ofactuation pressure that is available. This is particularly useful whenelectrostatic actuation is used that inherently has very limited amountsor levels of actuation pressure that can be generated with thisactuation method. Noteworthy is that without the feature ofpressure-balancing as shown in FIGS. 6(a) and 6(b), the actuation methodwould have to overcome the mechanical stiffness of the membrane 84 andthe pressure of the fluid, which can be substantial. However, withpressure balancing, even if the pressure of the fluid is many timeslarger in magnitude than the electrostatic pressure that can begenerated during actuation, the microvalve 70 membrane can still beactuated as shown in FIG. 6(b).

The important distinction between the micro-valve 50 shown in FIGS.5(a)-5(c) and the micro-valve 70 shown in FIGS. 6(a) and 6(b), is thatthe micro-valve 50 in FIGS. 5(a)-5(c) is a normally open micro-valve 50,wherein when in an un-actuated state or resting state, fluid is allowedto flow freely through either of the two inlet ports 53 and 54, throughthe micro-valve 50 chambers 51, and through the outlet port 57. Incontrast, the micro-valve 70 shown in FIGS. 6(a) and 6(b) is a normallyclosed micro-valve 70 at least for inlet port two, 73, when in anun-actuated state.

Additionally, as seen in FIGS. 5(b) and 5(c), actuation of themicro-valve 50 to close either of the inlet ports, 53 and 54, requiresthe application of separate applied voltages 65 or 68, whereas themicro-valve 70 shown in FIGS. 6(a) and 6(b), requires only one appliedvoltage potential 85 to actuate the micro-valve. Therefore, themicro-valve 70 shown in FIGS. 6(a) and 6(b) has a less complicatedapplied voltage requirement compared to the micro-valve 50 shown inFIGS. 5(a)-5(c).

As noted above, the micro-valve 50 and 70 devices shown in FIGS.5(a)-5(c) and FIGS. 6(a) and 6(b) employ electrostatic actuation as themethod for actuating the devices 50 and 70. However, other means can beemployed for actuation in either design configuration including:piezoelectric; bimetallic; shape-memory alloy, and thermo-pneumatic.

For example, shown in FIGS. 7(a) and 7(b) is a micro-valve 90 of thepresent invention having a similar design configuration as shown inFIGS. 6(a) and 6(b), but instead the micro-valve 90 uses piezoelectricactuation rather than electrostatic actuation. The 3-way micro-valve 90shown in FIGS. 7(a) and 7(b) is piezoelectrically-actuated and alsopressure-balanced. In FIG. 7(a), the micro-valve is shown an un-actuatedstate with inlet port one is an “open” state and connected to the outletport, thereby allowing fluid to flow through inlet port one, through themicro-valve, and through the outlet port. In this state, inlet port twois in a “closed” state and no fluid can flow through this port. In FIG.7(b) the device is shown actuated state with inlet port two in an “open”state and connected to the outlet port, thereby allowing fluid to flowthrough inlet port two, through the micro-valve, and through the outletport. In this state, inlet port one is in a “closed” state and no fluidcan flow through this port.

The micro-valve 90 shown in FIG. 7(a) is shown in the un-actuated state,that is, with no power applied to the actuator. The micro-valve 90 hastwo inlet ports that are inlet port one 94 and inlet port two 93. Thereis one outlet port 97. In the un-actuated state shown in FIG. 7(a), themicro-valve 90 has inlet port one 94 fluidically connected to the outletport 97 and inlet port two 93 is closed to the flow of fluid throughthis inlet port 93 and consequently through the micro-valve 90.

The micro-valve 90 shown in FIG. 7(a) is composed of a bottom substratelayer 96, a top substrate layer 95, and middle substrate layers 110.Middle substrate layers 110 may be composed of a plurality of layers asshown in FIGS. 7(a) and 7(b), so as to implement a configuration thatallows the inclusion of a piezoelectric layer 105 in combination withelectrode and electrical interconnection layers 106 and 107.Additionally, depending on the exact design configuration details,middle substrate layers may also include one or more insulating layers102 and 108 on either sides of the electrode and electricalinterconnection layers 106 and 107, and an insulating layer 109 toseparate the electrode and electrical interconnection layers 106 and 107where the piezoelectric layer 105 is not present.

An electrically insulating layer 98 may be present to electricallyinsulate the top substrate layer 95 from the middle substrate layers110, and an electrically insulating layer 99 may be present toelectrically insulate the bottom substrate layer 96 from the middlesubstrate layers 110. The micro-valve device 90, has a fluidic chamber91, wherein the fluid to be controlled by the micro-valve 90 can passthrough. Inside the flow chamber 91 of the micro-valve 90, is located amechanically-compliant membrane 112. That is, the membrane 112 can bedeflected under the action of an actuation force of sufficientmagnitude. The membrane 112 may or may not be electrically conductive,and as shown in FIGS. 7(a) and 7(b), may be composed of a multiplicityof layers (one or more layers) including: a silicon layer 114, one ormore piezoelectric layers 105, and electrode layers 106 and 107. Inother design and device configurations, the silicon layer 114 may bereplaced with an alternative material layer or layers, or may be omittedcompletely using only a piezoelectric layer 105 and electrodes 106 and107 in the membrane. Additionally, the silicon layer 114 may be composedof an alternative material layer and may also be in direct contact withthe lower sealing ring 103 when the micro-valve 90 is un-actuated. Thatis, in an alternative configuration, the silicon layer 114 is below thepiezoelectric layer 105 and the electrode layers 106 and 107, ratherthan on top as shown in FIGS. 7(a) and 7(b). Additionally, depending onthe exact details of the microvalve 90 design the silicon layer 114, thepiezoelectric layer 105, as well as the electrode layers 106 and 107,may be patterned in various shapes and sizes in order to obtain specificdesign requirements.

The membrane 112 has openings 92 that fluidically connect the inlet port94 to the outlet port 97 when the micro-valve 90 is not actuated asshown in FIG. 7(a). As shown in FIG. 7(a), the electrode and electricalinterconnection layer 107 is connected to an electrical terminal 101.Additionally, electrode and electrical interconnection layer 106connected electrical terminal 100. Importantly, in FIG. 7(a), theelectrical terminals, 100 and 101, are not connected to an appliedvoltage, since the micro-valve shown in FIG. 7(a) is in the un-actuatedstate.

The micro-valve 90 shown in FIGS. 7(a) and 7(b) has sealing rings (orsurfaces or valve seats), 103 and 104, whose purpose is to reduce oreliminate leakage of fluid through the ports when the valve is in aclosed position. The sealing rings 103 and 104 also help to reducestiction effects, whereby the membrane 112 stays stuck to the sealingrings 103 or 104 when it is desired that the membrane 112 separate fromthe sealing rings 103 or 104.

An actuated state of the micro-valve 90 is shown in FIG. 7(b). Anapplied voltage potential 111, V, is applied across electrical terminals100 and 101 connected to the electrode and electrical interconnectlayers 106 and 107 across the piezoelectric layer 105 and acts as theactuator on the membrane layers 112. The polarity of the applied voltage111 shown in FIG. 7(b) has the positive side of the voltage potential111 applied to terminal 101 and the negative side of the voltagepotential 111 applied to terminal 100. However, the applied voltage 111can be reversed with the same effect on actuation of the micro-valve 90.Additionally, one side of the applied voltage potential 111 could beconnected to ground also with the same effect on actuation of themicro-valve 90.

When an electrical voltage potential is applied across the terminals 100and 101 of the micro-valve 90, as shown in FIG. 7(b), the electricalfield created by the applied voltage potential 111 results in apiezoelectric force (not shown), whereby a strain is produced in thepiezoelectric material layer 105. This strain in the piezoelectric layer105 that part of the membrane layers 112, also causes a strain themembrane layers 112 due to the mechanical coupling of the membranelayers 112 to the piezoelectric layer 105. The consequence of thisstrain is that the layers of the membrane 112 deflect upwards so as toopen the inlet port one 93 of the micro-valve 90 to the flow of fluid.That is, the membrane layers 112 deflect upwards under the action of thestrain induced in the piezoelectric layer 105.

Since the membrane layers 112 are substantially mechanically compliant,the membrane layers 112 under the piezoelectric force will deflecttowards the top substrate layer 95 if the piezoelectric forces arelarger than the mechanical stiffness of the membrane layers 112. If theapplied voltage 111 across electrical terminals 100 and 101 issufficiently large in magnitude, the membrane layers 112 will deflecttoward and eventually touch the sealing ring 104. The touching of themembrane layers 112 to the sealing ring 104 is shown in FIG. 7(b). Whenthe membrane layers 112 make sufficient contact to the sealing ring 104,the micro-valve 90 is in a fully actuated state, whereby the inlet portone 94 is closed to the flow of fluid. In this actuated state, inletport two 93 is open and fluid can flow into this port, through themicro-valve 90 bottom part of the chamber 91, through the openings 92 inthe membrane layers 112, through the top part of the micro-valve 90fluid chamber 91, and through the outlet port 97. Therefore, in thisstate, inlet port one 94 is closed to fluid flow, inlet port two 93 isopen to fluid flow, and outlet port 97 is open to fluid flow.

The micro-valve 90 shown in FIG. 7(b) can be returned to the un-actuatedstate, shown in FIG. 7(a), by turning off or removing the appliedvoltage potential 111. When the voltage potential 111 is removed, thepiezoelectric forces on the membrane layers 112 dissipate and eventuallygo to zero. In this condition, the mechanical stiffness of the membranelayers 112 become larger than the piezoelectric forces and the membranelayers 112 will return to the un-deflected state, as illustrated in FIG.7(a).

An important different between the electrostatically-actuatedmicro-valve 50 and 70 shown in FIGS. 5(a)-5(c) and 6(a) and 6(b), andthe piezoelectrically-actuated micro-valve 90 shown in FIGS. 7(a) and7(b), is that the electrostatic actuation phenomena is non-linear,whereby the deflection of the membranes 64 and 84 is a non-linearfunction of the applied voltage potential 68 and 85. Additionally, oncethe membranes 64 and 84 have deflected a little over ½ of the totaldistance between the membrane 64 and 84 and substrate 55 and 75, themembrane 64 and 84 snaps to the fully actuation position due to theelectrostatic pull-in phenomena. In contrast, the piezoelectric actuatorshown in FIGS. 7(a) and 7(b) has a more linear deflection of themembrane with the applied voltage potential.

Another distinction of the micro-valve 90 shown in FIGS. 7(a) and 7(b)compared to the micro-valves 50 and 70 shown in FIGS. 5(a)-5(c) and 6(a)and 6(b) is that the piezoelectric actuation of the micro-valve 90 willtypically generate more actuation force than will an electrostaticactuator. The consequence of this higher actuation force is that themicro-valve 90 will have less probability of so-called “stiction”effects, whereby the membrane 112 stays stuck to the sealing ring 103and 104.

As noted above, an important feature of the micro-valve 90 shown inFIGS. 7(a) and 7(b) is the pressure-balancing scheme of the device 90.Specifically, the inlet fluid pressure inside the micro-valve 90 fluidchamber 91 is present on most of both sides of the membrane layers 112,with the exception of the area inside the sealing ring of inlet port two103. Consequently, there is a nearly equal fluid pressure over bothsurfaces of the membrane layers 112 with the result that the fluidpressure is balanced over both sides of the membrane layers 112.Therefore, if the fluid pressure is balanced, as shown in FIGS. 7(a) and(b), the micro-valve 90 can be actuated, as shown in FIG. 7(b), with anactuation pressure that is substantially less than the pressure of thefluid.

Noteworthy is that without the feature of pressure-balancing, as shownin FIGS. 7(a) and 7(b), the actuation method would have to overcome themechanical stiffness of the membrane layers 112 and the pressure of thefluid, which can be substantial. However, with pressure balancing, evenif the pressure of the fluid is many times larger in magnitude than thepiezoelectric force that can be generated during actuation, themicro-valve 90 membrane layers 112 can still be actuated, as shown inFIG. 7(b).

The micro-valve 90 shown in FIGS. 7(a) and 7(b) is a normally-closedmicro-valve 90, wherein inlet port two 93 is closed to the flow of fluidwhen the micro-valve 90 is an un-actuated state or resting state.

It is important to note that while an embodiment of a normally-closedmicro-valve 90 is shown in FIGS. 7(a) and 7(b), a normally-open designconfiguration of a pressure-balanced micro-valve, such as shown in FIGS.5(a)-5(c) using piezoelectric actuation, is also readily possible withthe use of one or more piezoelectric layers, so as to be part of thepresent invention.

While the micro-valves shown in FIGS. 7(a) and 7(b) uses piezoelectricactuation, it is understood that other methods of actuation can besubstituted for piezoelectric actuation including: bi-metallicactuation; shape-memory alloy actuation; thermo-pneumatic actuation; andothers, and are covered under the present invention.

Method of Fabrication of 3-Way Pressure-Balanced Microvalve

The method of implementation of the pressure-balanced microvalve isillustrated in cross-sections of the substrate at various points in thefabrication process sequences 120, 150 and 160 of the micro-valve asshown in FIGS. 8(a)-8(h), 9(a)-9(e) and 10(a) and 10(b). The micro-valvefabrication process sequences 120, 150 and 160 shown in FIGS. 8(a)-8(h),9(a)-9(e) and 10(a) and 10(b) are for the implementation of anelectrostatically-actuated pressure-balanced micro-valve, but can bemodified so as to implement micro-valves using other methods ofactuation such as piezoelectric-actuation, bimetallic actuation,shape-memory alloy actuation, thermo-pneumatic actuation, etc.

The micro-valve process sequence 120 begins in FIG. 8(a)-8(h) with asubstrate 121. The substrate 121 can be made of silicon, oralternatively any material compatible with the fabrication process andmaterials, such as other semiconductors, metal, glass, polymer, orceramic. The surface of the substrate 121 may be doped using eitherdiffusion or implantation so as to make the surface more electricallyconductive (not shown). This doping may be masked in certain regions ofthe substrate 121 surface. This can be achieved by depositing a maskinglayer, performing photolithography on the masking layer, followed byetching of the masking layer, followed by introduction of the dopantsinto the unmasked regions of the surface of the substrate 121. Analternative to introducing dopants into the surface of the substrate 121is to deposit an electrically conductive material layer (not shown) ontothe surface of the substrate 121. This electrically conductive layer maybe patterned using photolithography followed by etching so as to patternthe electrically conductive layer into the shape and pattern desired.

Subsequently, a layer of electrically insulating material 122 isdeposited onto the surface of the substrate 121. The electricallyinsulating material layer 122 can be made from low-stress siliconnitride (LSN) as well as other material layer alternatives such assilicon dioxide (SiO2), alumina, oxy-nitride, as well as any thin filmmaterial layer that is electrically insulating. The thickness of theelectrically insulating material layer 122 can vary, depending on theexact device design, cost and time considerations, as well as technologyconsiderations. This electrically insulating layer 122 may be patternedusing photolithography and etching to open areas 124 in the layer 122 soas to make electrical contact to the underlying electrically conductivesubstrate 121 or the underlying electrically conductive layer previouslydeposited (not shown) and possibly patterned as described above. This isshown in FIG. 8(b).

Next, a layer of material 123 that acts as a sacrificial material layer123 is deposited on top of the electrically insulating layer 122 thatwas previously deposited onto the substrate 121. This sacrificialmaterial layer 123 can be composed of phosphosilicate glass (PSG) or anymaterial type compatible as a sacrificial layer with the other materialsused in fabrication and suitable for microfabrication, such as glasses,ceramics, metals, semiconductors, polymers, etc. The thickness of thissacrificial layer 123 can vary depending on the exact design, cost andtime considerations, as well as technology considerations. Subsequently,this layer 123 has photolithography performed on it, followed by etchingto pattern the layer 123 as shown in FIG. 8(c).

Subsequently, a layer 125 of electrically conductive material isdeposited that acts as a structural layer 125 of the micro-valve. Thislayer 125 can be composed of polycrystalline silicon (polysilicon), aswell as any material type compatible with the other materials used infabrication and suitable for microfabrication, such as semiconductors,metals, semi-metallic ceramics, etc. The thickness of this structurallayer 125 can vary, depending on the exact design, cost and timeconsiderations, as well as technology considerations. This structurallayer 125 may be doped so as to make it higher in electricalconductivity. Subsequently, this structural layer 125 hasphotolithography performed on it, followed by etching to pattern thelayer 125 as shown in FIG. 8(d). During the patterning and etching ofthe structural layer 125, holes 126 that fluidically connect the top andbottom sections of the micro-valve chambers may be made in this layerstructural 125. These holes 126 in the structural layer 125 enable thepressure balancing of the micro-valve membrane that will be made fromthe structural layer 125.

Subsequently, a thin material layer 127 is deposited that will act as astrain-biasing layer 127 on the underlying structural layer 125. Thisstrain-biasing layer 127 will have an internal or residual stress thatwill cause the underlying structural layer 125 to slightly strain. Thisstrain-biasing layer 127 can be made of Chromium (Cr), as well as anymaterial layer type that is compatible with the other materials used infabrication and suitable for microfabrication, such as semiconductors,metals, ceramics, etc. The thickness of this strain-biasing layer 127can vary, depending on the exact design, cost and time considerations,as well as technology considerations. This stain-biasing layer 127 willbe patterned as shown in FIG. 8(e) using photolithography followed byetching as are well known in the art. Alternatively, the strain-biasinglayer 127 may be patterned using lift-off whereby a photosensitivepolymer is first deposited and exposed to patterned the photosensitivepolymer, then the strain-biasing layer 127 is deposited, and then, thephotosensitive polymer is removed thereby only leaving thestrain-biasing layer 127 in those areas where the photosensitive polymerwas not present over the surface of the substrate. “Lift-off” is awell-known method for patterning material layers.

Next, an electrically conductive layer 128 of material will be depositedto form metal areas that can act as electrical bonding pads and also asa wafer-to-wafer bonding layer. This electrically conductive materiallayer 128 may be made of gold, as well as any material layer type thatis compatible with the other materials used in fabrication, and that issuitable for microfabrication, electrically conductive, and can be usedin wafer-to-wafer bonding. If gold is used as the electricallyconductive layer 128, then a very thin adhesion layer (not shown in FIG.8(f)), such as Chromium or any suitable adhesion material layer, may bedeposited prior to the deposition of the layer 128 to ensure goodadhesion of the layer 128 to the underlying layers 125 on the substrate121. The thickness of this electrically conductive layer 128, andaccompanying adhesion layer, if used, can vary, depending on the exactdesign, cost and time considerations, as well as technologyconsiderations. The electrically conductive layer 128 (and accompanyingadhesion layer, if used) is appropriately patterned as shown in FIG.8(f). This layer 128 will be patterned as shown in FIG. 8(f) usingeither photolithography followed by etching, or lift-off, both of whichare well known in the art.

Note that an electrically conductive layer 128 is also deposited andpatterned in the regions of the electrically insulating layer 122 thatwere opened up to expose either the electrically conductive substrate121 or an electrically conductive material layer (not shown) that wasdeposited onto the substrate 121. This layer 128 deposited directly ontothe substrate 121 in these regions will allow electrical connection tothe substrate 121 during micro-valve operations.

Photolithography is then performed on the backside of the substrate 121,and then a through-wafer deep, high-aspect ratio etch, such as Deep,Reactive-Ion Etch (DRIE), is performed to form one or more micro-valvefluid ports 129, as shown in FIG. 8(g). Next, the layer 123 that acts asa sacrificial layer 123 is removed, thereby releasing the structurallayer 125 as shown in FIG. 8(h). Note that the strain-biasing layer 127causes strain in the structural layer 125 upwardly. This upwarddeflection will enable the micro-valve to be normally closed when thefabrication is completed.

The process sequence 150 continues in FIG. 9(a)-9(e) on a secondsubstrate 151, as shown in FIG. 9(a). The second substrate 151 to beused in the process sequence 150 can be made of silicon, oralternatively, any suitable substrate material compatible with thefabrication process 150 and materials, such as other semiconductors,metal, glass, polymer, or ceramic.

A thin layer of Chrome, or other appropriate material layer, is thendeposited that acts as an adhesion layer (the adhesion layer is notshown in FIG. 9(b) since the layer is so thin). This is followed by thedeposition of a layer of metal 152, such as gold, that can act to helpperform wafer-to-wafer bonding later in the process sequence. The metaland adhesion layers 152 are patterned as shown in FIG. 9(b) usingphotolithography, followed by etching, or are patterned using lift-off,as shown in FIG. 9(b). Bother techniques are well known in the art.

Next, photolithography is performed on the substrate 151 followed by adeep, high-aspect ratio etch, such as DRIE, partially into the surfaceof the substrate to form part of the fluid chamber 153 of themicro-valve, as shown in FIG. 9(c).

Subsequently, another photolithography and deep, high-aspect ratio etch,such as DRIE, is performed partially into the surface of the substrate151 to form the valve seat or sealing ring 154 and complete the makingof the fluid chamber 153 of the micro-valve as shown in FIG. 9(d).Alternatively, a material layer for implementing the sealing ring 154may be deposited, patterned and etched so as to form the shape andstructure of the sealing ring 154.

The purpose of the sealing ring 154 is two-fold: the first is to providebetter fluid sealing when the micro-valve is closed; and the second isto reduce the stiction effects when the micro-valve is actuated (thatis, opened by separating the micro-valve membrane from the sealing ring154 surface). Typically, the shape of the sealing ring 154 is to haveeither a narrow width and/or a sharp edge on the surface. The reason forthis preferred shape is that it will reduce leakage through themicro-valve when the device is closed to fluid flow and it will alsoreduce stiction effects between the sealing ring 154 and membrane thatmay make opening the micro-valve more difficult when the device is to beactuated. The substrate with the sealing rings 154 present is shown inFIG. 9(d).

Photolithography is then performed on the backside of the secondsubstrate 151, followed by the performance of a deep, high-aspect ratioetch, such as DRIE, on the substrate 151 completely through the backsideof the substrate 151 to form the microvalve ports 155 and 156, as shownin FIG. 9(e). An inlet port 155 and an outlet port 156 can be made withthe same etching. Additionally, a through-substrate via or opening ismade in the substrate 157 during this etch that will allow electricalconnection to the substrate 121 for electrical actuation of themicro-valve.

The first substrate from FIG. 8(h) and the second substrate from FIG.9(e) are then brought together and bonded as shown in FIG. 10(a), byaligning the Gold bonding areas 128 and 152 on the two substrates 121and 151 and performing a thermo-compression bond 162 thereby resultingin the completed micro-valve structure 163, as shown in FIG. 10(b).

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of fabricating a three-waypressure-balanced micro-valve device, the method comprising: providing abottom substrate, micomachining the bottom substrate so as to form inthe bottom substrate a bottom fluid chamber having a depth extendingpartially into the bottom substrate, forming in the bottom substrate atleast one fluid port that passes completely through the bottomsubstrate, so as to fluidically connect to the bottom fluid chamber,providing a top substrate, micomachining the top substrate so as to formin the top substrate a top fluid chamber having a depth extendingpartially into the top substrate, and forming in the bottom substrate atleast at least one fluid port that passes completely through the bottomsubstrate so as to fluidically connect to the bottom fluid chamber, andproviding a middle substrate, and thinning the middle substrate so as tobe a membrane layer in the region of where the fluid chamber is located.2. The method of claim 1 for fabricating a three-way micro-valve ,wherein either the top or bottom substrate is micromachined to makeopenings extending completely through the micromachined substrate toprovide an electrical connection to the membrane layer for enablingelectrical actuation of the micro-valve.
 3. The method of claim 1 forfabricating a three-way micro-valve, wherein the fluid ports fabricatedcompletely through the top and bottom substrates are each made using adeep, high-aspect ratio etch.
 4. The method of claim 3 for fabricating athree-way micro-valve, wherein the etch used is a Deep, Reactive-IonEtch (DRIE).
 5. The method of claim 1 for fabricating of a three-waymicro-valve, wherein the fluid chambers made in the top and bottomsubstrates are made using a deep, high-aspect ratio etch.
 6. The methodof claim 5 for fabricating of a three-way micro-valve, wherein the etchused in a Deep, Reactive-Ion Etch (DRIE).
 7. The method of claim 1 forfabricating of a three-way micro-valve, wherein the membrane is made ofa deposited layer of poly-crystalline silicon (polysilicon).
 8. Themethod of claim 1 for fabricating of a three-way micro-valve furthercomprising employing material layers that strain-bias the membrane so asto result in a normally-closed micro-valve configuration.
 9. The methodof claim 1 for fabricating of a three-way micro-valve, wherein the topand bottom substrates are made of silicon.
 10. The method of claim 1 forfabricating of a three-way micro-valve, wherein piezoelectric materiallayers and top and bottom electrodes on both sides of the piezoelectriclayer are made that enable the micro-valve to be actuated usingpiezoelectric means of actuation.
 11. The method of claim 1 forfabricating of a three-way micro-valve, wherein the top and bottomsubstrates are made from glass, metal, semiconductor, or a ceramic, or acombination thereof.